Heavy duty tires widely employed for trucks, buses, and the like are a so-called single-crown type in which the profile line of a surface of a tread portion (tread profile line) is formed by a single arc having an arc center on a tire equatorial plane. However, such a single-crown tire has a large tire radius difference between the tire equatorial plane and the tread edge. Thus, there is a problem that a slip occurs between the tread surface of the tread edge side and the road surface, thereby resulting in so-called shoulder wear m1 (shown in FIG. 7(A)).
Accordingly, Patent Literatures 1, 2, and others each suggest a tire that has a tread profile line (a) as schematically shown in FIG. 8(A), for example. The tread profile line (a) is divided into a crown area profile line part (a1) on the tire equatorial plane side and a shoulder area profile line part (a2) on the tread edge side. The crown area profile line part (a1) is formed by a first arc (b1) with a radius of curvature (r1) having an arc center on a tire equatorial plane (Co). The shoulder area profile line part (a2) is formed by a second arc (b2) with a radius of curvature (r2) larger than the first arc (b1) or a straight line (b3). In such a tire, compared to the single-crown tire, a tire radius difference A between the tire equatorial plane side and the tread edge side is smaller, and thus occurrence of shoulder wear (m1) (shown in FIG. 7(A)) is suppressed.
As shown in FIG. 7(B), however, it has been found that so-called triangular wear (m2) occurs at shoulder blocks (d) disposed in the shoulder region (a2). The triangular wear (m2) develops in a triangular shape at corner portions (p) on an earlier ground-contact side and a tire axially outside of the shoulder blocks (d) as origin points.
A possible cause of occurrence of the triangular wear (m2) is as described below. Specifically, when the shoulder area profile line part (a2) is formed by the second arc (b2) with the large radius of curvature (r2) or the straight line (b3), in ground-contact pressure distribution of the shoulder block (d) as illustrated in FIG. 8(B), a ground-contact pressure rising portion (k) with a peak-like rise of ground-contact pressure occurs at the tire axially outside end of the shoulder block (d). On the other hand, the front tire is a driven wheel, and thus at the rotation of the tire, a slip occurs between the road surface and the tire on the earlier ground-contact side of the block. The amount of wear is almost proportional to the product of ground-contact pressure and slip amount. Therefore, it is considered that the triangular wear (m2) develops, within the blocks, at the corner portions (p) on the tire axially outside end with a peak-like rise in ground-contact pressure and on the earlier ground-contact side with a larger slip, as origin points of wear.